Anomalous occurrence of immunoreactive calcitonin cells in the thymus of the rat

Abstract

In a study of the effect of pinealectomy on thyroid C-cell number, 8 animals out of 66 were found to have thymic tissue in close association with the thyroid. Cells containing immunoreactive calcitonin were found in all of the thyroids but in only one of the 8 pieces of thymus. These cells found in a piece of thymic tissue associated with the right thyroid lobe were located immediately under the capsule and did not form or associate with follicles. Unlike the other animals the rat with thymic calcitonin cells had an unequal distribution of C-cells between the left and right thyroid lobes, but the total number of thyroidal C-cells was the same as that of the other rats. Since the thymus proper was not examined in these 66 animals, ten additional rats were taken for such a study. Thyroid-associated thymic tissue was found in three of these, but none of these thymi showed any immunoreactive cells.

Number and size of rat thyroid C cells: No effect of pinealectomy

“…Due to some incomplete series of sections, the number of animals given in each group differs from that in Materials and Methods. One animal in the sham series had some C cells anomalously located in the thymus (McMillan et al, 1982). The total volume of the C cell region and the number of C cells in the thyroid gland of this animal were at the mean of those of the other rats in this group in spite of the fact that these were greatly reduced on the affected side.…”

“…Hence calcitonin measurements carried out in one thyroid lobe can be correlated with C cell number in the other, and hemithyroidectomy will remove roughly half of the C cell population, the total population being on the order of 700,000 cells per gland. One exception (due to anomalous development) to the even distribution of C cells has been observed (McMillan et al, 1982). The number of C cells per mm3 of thyroid tissue is 63,000 in the rat but 30,600 in 8-week-old mice (Wechbanjong et al, 1979).…”

Endocrinology of the Vertebrates

“…In mammals, the ultimobranchial anlage is greatly transformed and the majority of cells become somewhat scattered to incorporate into the thyroid gland, as the parafollicular C (calcitonin-producing) cells. In some species, C cells are also found in the parathyroid and thymus glands (439,581). The gland itself may be arranged in a follicular fashion, as in elasmobranchs, or as bunches of cell masses intermingled with blood vessels and small follicles.…”